1. Field of the Invention
The present invention relates to a water-decomposable absorbent article for sanitary napkins, pantiliners, incontinence pads, diapers, etc.
2. Description of the Related Art
Recently, absorbent articles disposable in flush toilets have come available, including, for example, sanitary napkins, pantiliners, incontinence pads, diapers, etc. For example, Japanese Unexamined Patent Publication (Kokai) Nos. Heisei 8-38547 and 8-19571 disclose water-decomposable absorbent articles comprising a water-decomposable absorbent layer, and water-decomposable surface and back layers between which the absorbent layer is sandwiched.
In these water-decomposable absorbent articles, the constituent layers are relatively firmly bonded to each other so as to prevent the articles from being loosened or broken to lose their shape during use. However, in case where the layers constituting them are bonded to each other with a high-strength adhesive, the absorbent articles used could not be readily decomposed in water in toilets. This is because the constituent layers could not be readily separated from each other in toilets, and therefore they will float in septic tanks and drains owing to air existing between respective constituent layers, and could not disperse in water. On the other hand, however, in case where the constituent layers are bonded to each other by lower bonding strength so as to ensure their decomposition in water, the absorbent articles will be loosened and could not keep their shape during use.
An object of the present invention is to provide a water-decomposable absorbent article which can surely keep its shape during use and can be easily decomposed in water when disposed of in toilets after use.
According to an aspect of the invention, a water-decomposable absorbent article may comprise a water-decomposable back layer, a water-decomposable and liquid-pervious surface layer, and a water-decomposable absorbent layer sandwiched between the back layer and the surface layer, wherein;
the absorbent article including an outer peripheral region being formed in a predetermined width spaced from a peripheral edge of the absorbent article, and an inner region located inside the outer peripheral region,
the absorbent layer and the back layer, and/or the absorbent layer and the surface layer are bonded to each other with a water-soluble or water-swellable adhesive therebetween in the inner region, and the interlayer bonding strength of the layers bonded with the adhesive in the inner region is higher than the interlayer bonding strength of the layers in the outer peripheral region, both in wet and in dry.
In this, the interlayer peeling rate of the constituent layers in wet may be higher in the outer peripheral region than in the inner region.
The absorbent article of the invention is so constituted that its interlayer bonding strength is higher in the inner region than in the outer peripheral region both in dry and in wet. Being so constituted, the constituent layers are hardly separated from each other and are hardly loosened both in dry and in wet while the absorbent article is used. Accordingly, the absorbent article well keeps its shape during use and is highly durable. In addition, the absorbent article is so specifically constituted that, while in wet, the interlayer bonding force in the outer peripheral region is low and the interlayer peeling rate is higher in the outer peripheral region than in the inner region. Therefore, when the absorbent article is, after used, disposed of in flush toilets, the constituent layers are readily separated from each other first in the outer peripheral region. As a result, air existing inside the inner region moves away through the thus-separated layers in the outer peripheral region to prevent the absorbent article from floating in septic tanks. Even though the interlayer bonding strength in the inner region is high and the constituent layers therein will be peeled slowly in wet, the interlayer peeling in the inner region can be promoted as triggered by interlayer peeling in the outer peripheral region, when the absorbent article sank in septic tanks. As a result, the absorbent article disposed of in toilets can be smoothly decomposed.
For example, the outer peripheral region has a width of from 2 to 25 mm inwardly from a peripheral edge of the absorbent article. The inner region is meant to indicate the region except for the outer peripheral region, and an adhesive is partially applied to the inner region.
In the outer peripheral region, the constituent layers are bonded to each other with a water-soluble adhesive therebetween, and the solubility in water of the adhesive in the inner region is preferably lower than that of the adhesive in the outer peripheral region.
In the outer peripheral region, the constituent layers are bonded to each other with a water-soluble adhesive therebetween, and the amount of the water-soluble adhesive applied to the unit area of the inner region may be larger than that of the adhesive applied to the unit area of the outer peripheral region.
In that case, the adhesives applied to the inner region and to the outer periphery region may be each made of preferably polyvinyl alcohol, and the applied amount may fall between 10 and 30 g/m2 in the outer peripheral region and the applied amount may fall between 30 and 200 g/m2 in the inner region.
In the absorbent article of the invention, the constituent layers in the outer peripheral region may be bonded to each other under pressure without interposing the adhesive. For example, in the outer peripheral region, the constituent layers may be bonded to each other via hydrogen bonding.